1. Field
Embodiments of the invention generally relate to an improved substrate processing system. Specifically, embodiments of the invention relate to a fast gas exchange system that is suitable for etching and/or deposition process.
2. Description of the Related Art
The fabrication of microelectronic devices includes a number of different stages, each including a variety of processes. During one stage, a particular process may include imparting a plasma to the surface of a substrate, such as a silicon substrate, to alter the physical and material properties of the substrate. This process may be known as etching, which may involve the removal of materials to form holes, vias, and/or other openings (referred to herein as “trenches”) in the substrate.
Plasma etch reactors are commonly used for etching trenches in semiconductor substrates. These reactors contain a chamber within which the substrate is supported. At least one reactive gas is supplied to the chamber and a radio frequency signal is coupled to the reactive gas to form the plasma. The plasma etches the substrate that is positioned within the reactor. The substrate may also be coupled to a radio frequency signal to bias the substrate during the etching process to enhance etching performance and trench profile.
Through silicon via (“TSV”) etching is a unique application that requires a low frequency bias and a low temperature environment to form deep trenches in a silicon substrate. One type of etching system may include in situ plasma etching. Using this type of etching system, a trench can be formed by alternating the removal and deposition of material on a substrate in a single reactor with a removing plasma and a deposition plasma. Another type of etching system may include remote plasma etching. Using this type of etching system, a trench can be formed as in the in situ system, except that the plasmas may be generated in a remote reactor prior to being introduced onto the substrate located in the primary reactor. In addition to the types of etching systems, the process of etching with each system may also vary. Some etching processes employ multi-step approaches, such as a time multiplexed gas modulation (“TMGM”) system or a Bosch system, that includes several recipe steps, such as etch and deposition step, or etch, flash, and deposition steps. The TMGM process etches a material for a period of time and then deposits a protective film upon the previously etched surface to protect the surface, typically the sidewalls of the trench, from further etching. These two steps are repeated as a deeper and deeper trench is formed. As the process development continues for smaller and deeper TSV geometry, the recipe may require fast switching between etching gas, deposition gas, passivation gas or cleaning gas. Therefore, the switching gases become more critical in controlling the etch profile, sidewall protection, selectivity, and etch rate (i.e., throughput).
For faster etch rates and smooth etch profile, faster switching of gases is needed. Faster switching means more duty cycles per unit time period. In conventional gas delivery systems, the speed of gas introduction to the processing chamber is limited by the valve switching speed due to the mechanical nature of the system. Additionally, a process recipe that requires gas switching at, for example, 0.2 second intervals, the gas switching valve will be cycled more than 78 million times annually. As the service life for a typical valve is about 3 million cycles, the need for expensive, high performance valves with extended service life or frequent valve replacement is required, which undesirably increases the chamber downtime for service and the cost of ownership.
Therefore, there is a need for an improved method and apparatus for etching.